1. Field of the Invention
The present invention relates to an anionic polymerization process of polymerizing an anionic polymerizable monomer with an anionic polymerization initiator, and a process for producing a polymer using this polymerization process.
2. Related Art of the Invention
Various investigations have been made on a process of subjecting a polar monomer such as a methacrylic acid ester or an acrylic acid ester to anionic polymerization. However, such a polar monomer has a moiety which receives nucleophilic attack easily, such as a carbonyl group. Upon anionic polymerization for the polar monomer, therefore, it is relatively difficult that a high living polymerization property is exhibited since there arises a side reaction of the monomer or an intermolecular cyclization reaction (so-called back biting) at the growing terminal of the resultant polymer.
It is suggested that when a polar monomer is subjected to anionic polymerization using an organolithium compound as a polymerization initiator, an organoaluminum compound is caused to be present in the polymerization system. According to this manner, the organoaluminum compound coordinates to the growing terminal. Thus, the growing terminal can be stabilized so that its nucleophilicity can be lowered. As a result, it appears that the living polymerization property upon the polymerization can be raised. As processes for performing anionic polymerization of a polar monomer in the presence of an organoaluminum compound, using an organolithium compound as a polymerization initiator, the following processes (1)-(6) are reported:
(1) a process of performing a polymerization reaction of a methacrylic acid ester in the presence of an organoaluminum compound such as trialkylaluminum or dialkyl(diphenylamino)aluminum in an aromatic hydrocarbon solvent, using t-butyllithium as a polymerization initiator (JP-B-H7-57766),
(2) a process of polymerizing a methacrylic acid ester in the presence of a specific organoaluminum compound having one or more bulky groups (for example, triisobutylaluminum or diisobutyl(2,6-di-t-butyl-4-methylphenoxy)aluminum) in a hydrocarbon solvent, using an organolithium compound such as t-butyllithium as a polymerization initiator (U.S. Pat. No. 5,180,799),
(3) a process of polymerizing methyl methacrylate in the presence of an organoaluminum compound, such as methylbis(2,6-di-t-butylphenoxy)aluminum, ethylbis(2,6-di-t-butylphenoxy)aluminum, isobutylbis(2,6-di-t-butylphenoxy)aluminum or tris(2,6-di-t-butylphenoxy)aluminum, in an aromatic hydrocarbon solvent, using an organolithium compound as a polymerization initiator (U.S. Pat. No. 5,656,704),
(4) a process of polymerizing a methacrylic acid ester or an acrylic acid ester in the presence of methylbis(2,6-di-t-butylphenoxy)aluminum or ethylbis(2,6-di-t-butylphenoxy)aluminum in toluene, using t-butyllithium as a polymerization initiator (Polymer Preprints, Japan, Vol. 46, No. 7, pp. 1081-1082 (1997) and Polymer Preprints, Japan, Vol. 47, No. 2, p. 179 (1998)),
(5) a process of polymerizing methyl methacrylate in the presence of trialkylaluminum in toluene, using t-butyllithium as a polymerization initiator (Makromol. Chem., Supplement. Vol. 15, pp. 167-185 (1989)), and
(6) a process of polymerizing methyl methacrylate in the presence of diisobutyl(2,6-di-t-butyl-4-methylphenoxy)aluminum in toluene, using t-butyllithium as a polymerization initiator (Macromolecules, Vol. 25, pp. 5907-5913 (1992)).
Furthermore, it is reported that when a polar monomer is subjected to anionic polymerization in the presence of an organoaluminum compound using an organolithium compound as a polymerization initiator, a certain additive is caused to be present in the polymerization system so that the rate of the polymerization can be increased or so that uniformity of the polymerization is improved and the molecular weight distribution of the resultant polymer can be narrowed. Such reports are, for example, about the processes (7) and (8).
(7) When a methacrylic acid ester is polymerized in the presence of trialkylaluminum in toluene using t-butyllithium as a polymerization initiator, the rate of the polymerization is improved and the molecular weight distribution of the resultant polymer is narrowed by adding to the polymerization system an ester compound, such as methyl pivalate or diisooctyl phthalate, in an amount of about 10% by weight of toluene (solvent). In the case in which a crown ether such as 12-crown-4 is added instead of the ester compound, the same improvement effects are exhibited. However, in the case in which tetrahydrofuran, 1,2-dimethoxyethane, N-methylpyrrolidine or the like is caused to be present instead of the ester compound, the improvement effects are not exhibited (Macromolecules, Vol. 31, pp. 573-577 (1998)).
(8) When a methacrylic acid ester or an acrylic acid ester is polymerized in the presence of an organoaluminum compound such as trialkylaluminum in a hydrocarbon solvent using an organolithium compound such as ethyl xcex1-lithioisobutyrate or t-butyllithium as a polymerization initiator, the rate of the polymerization is improved and the molecular weight distribution of the resultant polymer is narrowed by adding to the polymerization system an ether compound such as triethylene glycol dimethyl ether (triglyme), dimethoxyethane or crown ether, or an organoquaternary salt such as tetraalkylammonium halide or tetraphenylphosphonium halide (International publication: WO98/23651).
As described as the above-mentioned processes (1)-(8), various suggestions are made on processes of anionic polymerization of a polar monomer in the presence of an organolithium compound and an organoaluminum compound. However, the polymerization initiators that are actually used in these processes are limited to specific compounds such as t-butyllithium and ethyl xcex1-lithioisobutyrate. This would be because it is considered that a high polymerization initiation efficiency and a high polymerization rate can be attained. However, t-butyllithium has mighty self-ignition ability, and has problems about safety thereof and handling performances upon transportation, storage and the like. Concerning ethyl xcex1-lithioisobutyrate, an operation for synthesizing it and a subsequent purifying operation are complicated. For these reasons, it is difficult to say that these polymerization initiators, which make it possible to attain a high polymerization initiation efficiency and a high polymerization rate, are suitable for use in an industrial scale. Besides, examples of specific experiments reported as the processes (1)-(8) include examples wherein polymerization initiation efficiency is insufficient for practical use.
In the case in which a polar monomer such as a methacrylic acid ester or an acrylic acid ester is block-copolymerized with another monomer, a living polymer resulting from the polymerization of the one monomer needs to have such a high living polymerization property that causes the polymerization of the other monomer to start. However, in order to exhibit such a high living polymerization property upon anionic polymerization in the presence of an organolithium compound and an organoaluminum compound, it is necessary in many cases to set the temperature upon the polymerization to a very low temperature, for example, about xe2x88x9260xc2x0 C. In such polymerization operation at a very low temperature, many facilities become necessary for cooling. Thus, industrial adoption of this operation is disadvantageous. Moreover, in the case in which an ester of a primary alcohol and acrylic acid, such as n-butyl acrylate, is used as the polar monomer upon polymerization, the living polymerization property upon the polymerization becomes especially low. By the inventors"" investigations, the following results were obtained: when an ester of a primary alcohol and acrylic acid was polymerized in a reaction system in the presence of trialkylaluminum and a crown ether or an organoquaternary salt as reported as the process (8) at a very low temperature of about xe2x88x9278xc2x0 C., the living polymerization property of the resultant polymer of the acrylic acid ester was lost; therefore, in the case wherein the polymer was subsequently brought into contact with another polar monomer such as methyl methacrylate, no polymerization was able to start. Furthermore, in the case in which an acrylic acid ester is polymerized at a very low temperature as described above, the resultant polymer of the acrylic acid ester has high steroregularity and high crystallinity. Thus, the polymer may be insufficient in flexibility. Therefore, in order to obtain an acrylic acid ester polymer having excellent flexibility, it is not preferred to perform the polymerization reaction at a very low temperature as described above. From these standpoints, there has not yet been found an industrially-profitable process for producing a block copolymer of a polar monomer, such as a methacrylic acid ester or an acrylic acid ester, in the actual situation.
From the above-mentioned standpoints, all of the following requirements are important for making anionic polymerization of a polar monomer profitable for industrial enforcement: the rate of the polymerization is high; the initiation efficiency of the polymerization is high; the range of a polymerization initiator which can be used is wide; the living polymerization property upon the polymerization is high (that is, the molecular weight distribution of the resultant polymer is narrow and the production ratio of a block copolymer in block copolymerization is high); and cooling conditions upon the polymerization can be made mild.
Therefore, a problem to be solved in the present invention is to provide in anionic polymerization of a polar monomer a polymerization process making it possible to attain a high polymerization initiation efficiency and a high polymerization rate, using a polymerization initiator relatively excellent in safety, availability, and handling performances, which process makes it possible to produce a polymer having a relatively narrow molecular weight distribution because a high living polymerization property can be exhibited even if a relatively high polymerization temperature (that is, a relatively mild cooling condition or a condition of a temperature near room temperature) is adopted, and which process is also useful for production of a block copolymer. Another problem to be solved in the present invention is to provide an industrially-profitable process for producing a polymer, using the above-mentioned polymerization process having such advantages described as above.
The inventors made eager investigations to solve the above-mentioned problems. As a result, it has been found that in the case wherein, at the time of polymerizing an anionic polymerizable monomer with an anionic polymerization initiator, a combination of a specific organoaluminum compound and a specific Lewis base is caused to be present in the polymerization system, it is possible to solve the problems about the above-mentioned aptitude of the polymerization initiator for industrial use (the safety, availability and handling performances), and the problems about the above-mentioned polymerization conditions and polymerization results (the temperature condition, polymerization initiation efficiency, polymerization rate and living polymerization property). Thus, the present invention has been made.
That is, a first aspect of the present invention is an anionic polymerization process, characterized in that when an anionic polymerizable monomer is polymerized with an anionic polymerization initiator, a tertiary organoaluminum compound (A) having in the molecule thereof a chemical structure represented by a general formula: Alxe2x80x94Oxe2x80x94Ar wherein Ar represents an aromatic ring, and at least one Lewis base (B) selected from the group consisting of an ether compound and a tertiary polyamine compound are caused to be present in the polymerization system wherein the polymerization is performed.
A second aspect of the present invention is a process for producing a polymer, which comprises polymerizing an anionic polymerizable monomer by the above-mentioned anionic polymerization process (for example, a process for producing a block copolymer, which comprises polymerizing two or more anionic polymerizable monomers by the above-mentioned anionic polymerization process).